Dremel 300 speed control Switch Faulty "I think" Help to bypass it.

Thread Starter

RodneyB

Joined Apr 28, 2012
697
I have a Dremel 300 which I use for drilling my printed circuit boards. I have the drill stand that goes with it.

For years I have not had a seconds problem with it.

Yesterday it just stopped, so I checked the brushes and they were almost non-existent. I had some made here and I fitted them.

When the drill was turned on it made a strange sound but was turning, I assumed that the brushes needed to be run in. However the drill got very hot. So I waited for it to cool down and then opened it up. There was lots of fine dust which I blew out and then basically I cleaned everything I could with isopropyl.

When I reassembled it the switch now does not work.

Can you give me some advice on how to go about repairing this machine. I would be happy right now to bypass the switch and buy a new one. At least if I get it running I know nothing else is wrong
 

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Thread Starter

RodneyB

Joined Apr 28, 2012
697
Need to see the PCB out of the housing completely.
Your picture is out of focus.
Sorry about that.

Please see attached photos taken again. On the back of the PCB I see the letters and numbers VSC 220V so I did an internet search and came up with the attached drawing. It looks Identical except mine is a 220 Volt machine.

If I bridge out the triac will I be able to test to see if the motor runs.
 

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MrAl

Joined Jun 17, 2014
7,849
Hi,

You do have to realize that when you wire it directly you get full speed all the time, which is somewhere around 30,000 rpm and that is quite fast. Some cutoff wheels only go up to 20,000 rpm safely.

As others have said, you can use a lamp dimmer. We did this a long time ago for someone who needed a speed control for a dremel that did not have one yet.
I also made one with some small parts and you could look on the web to find a circuit. It's just a triac phase control circuit.

Alternately in a pinch you can try to find a light bulb that when in series with the motor alllows a lower, more manageable speed.
Also, if you have a variac around you can use that with great success once the motor is wired directly.
 
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